test external network get fail

issue on test external network in review [0]

on test a few result are:

23:16:14 ------------------------------------------------------------------------------
23:16:14 SNAT - TCP connection to External Gateway From SNAT VM Instance1 :... | FAIL |
23:16:14 'nc: 10.10.10.250 (10.10.10.250:12345): Connection timed out
23:16:14 $' does not match 'Test Server Data'
23:16:14 ------------------------------------------------------------------------------
23:16:29 SNAT - UDP connection to External Gateway From SNAT VM Instance1 :... | FAIL |
23:16:29 '10.10.10.250 (10.10.10.250:12345) open
23:16:44 $' does not match 'Test Server Data'

[0] review: https://git.opendaylight.org/gerrit/#/c/63951